Our design is a prospective study of an immunization protocol with recombinant Hepatitis Surface antigen vaccine in non-immunized healthy stressed and non-stressed adults, females and males, young (21-40 yrs) and elderly (55-80 yrs). Neuroendocrine and immune parameters will be measured at baseline and subsequently at 1,4,24, and 32 weeks after immunization. Neuroendocrine parameters will include plasma ACTH, cortisol, catecholamines, pituitary GH and prolactin, lymphocytic GH gene expression, DHEA and salivary cortisol. Multiple sampling of blood, saliva and urine will be done in a 24 hour period to ascertain diurnal and nocturnal hormonal variations. The immune response to the vaccine will be assessed, in vivo by the antibody response after immunization. In addition, the cellular response to the vaccine will be assessed in vitro by analyzing the proliferation response and cytokine production by HBsAg antigens stimulated PBMC. In addition, monokines produced by HBsAg stimulated antigen presenting cells (APC) such as Interleukin-12 and Interleukin-1-Beta will be measured. The modulatory effect of ACTH and GH on the antigen specific response of cytokines will be studied. A psychological assessment will be done to measure the stress levels of the study subjects, coping skills and life stressors through validated questionnaires such as: Perceived Stress Scale, Impact of Life Events scale and Satisfaction with Life among others.